The invention relates to a television and radio antenna in motor vehicles in the meter (high) and decimeter (very high) frequency ranges. The invention is based on a multi-antenna system for creating an antenna diversity system.
The Prior Art
Radio and Television multi-antenna systems are described, for example in European Patent EP 0 269 723; German Patents DE 36 18 452; DE 39 14 424; DE 37 19 692; P 36 19 704; and may employ different types of antennas such as a rod, windshield, windowpane or similar antennas. One problem with these patents is that with an adequate HF-decoupling of the antennas, reception interferences occur in the receiving field when the vehicle moves into different positions. Such reception interferences occur in connection with transient drops in the reception level because of multi-path propagation of the electromagnetic waves. This effect is explained by way of example in EP 0 269 723 with the help of FIGS. 3 and 4.
To overcome these problems, a scanning antenna diversity system is used to switch from one antenna to another when a reception interference occurs in the operating antenna. These diversity antennas provide an additional antenna to keep the number of level drops or signal breaks leading to reception interferences in a predetermined receiving field as low as possible on the receiver input. Diversity antennas are extensively effective, but require an indicator for the interference taking place, equipment for changing over the antennas, as well as two antennas. Unfortunately, the interference indicator and the required change-over equipment can be quite expensive. On the other hand, it is desirable to raise the receiving quality as high as possible, especially when an antenna diversity system is employed.
When trying to overcome these breaks in reception, statistical modeling by Rayleigh has been used to map the signal paths of radio and television waves. From these statistical models of the electromagnetic waves incident on the vehicle, it is known that locally limited level breaks of the receiving signal occur with each antenna present on the vehicle. When driving, these level breaks cause short-term reception interferences which are perceived as extremely annoying when receiving with only one antenna.